1. Field of the Invention
The present invention relates to a power supply, particularly to a secondary side-driven half-bridge power supply.
2. Description of the Related Art
In the current power supply industry, the switched-mode power supply usually adopts a half-bridge power source circuit because the induction magnetic field can work in the first and third quadrants under the half bridge architecture. The forward type or flyback type architecture can only work in the first quadrant. Therefore, the half-bridge power source circuit has a much higher efficiency.
In the current power supply industry, the PWM (Pulse Width Modulation) controller is often arranged on the secondary side. A separating element is used to amplify a small duty-cycle signal waveform, and the amplified signal is used to drive power transistors on the primary side and then drive a half-bridge transformer. Refer to FIG. 1. The power transistors 10 are usually formed of two bipolar junction transistors. During the switching activities of a bipolar junction transistor, the current usually flows through a transistor area, and power is thus consumed therein. When the switching frequency of a power supply is increased, the performance of bipolar junction transistors is further degraded. Besides, the current semiconductor industry lays stress on the fabrication of metal oxide semiconductor field effect transistors; the bipolar junction transistors are obsolescing and will no more play an important role in the future technology.
Accordingly, the present invention proposes a half-bridge power supply to overcome the abovementioned problems.